Abstract

Boiling water reactor (BWR) reactor pressure vessel nozzle-to-shell welds and nozzle blend radii are inspected in accordance with ASME Code, Section XI, which requires 100% inspection during each 10-year in-service inspection interval. ASME Code Case N-702-1 provides inspection relief to 25% of the nozzle population every 10 years. The NRC placed limitations on N-702-1 which excluded feedwater nozzles and control rod drive return nozzles and only allowed implementation for up to 40 years of plant operation. N-702-1 has been used by many utilities for inspection relief, resulting in substantial time, dose and cost savings related to inspections. N-702 was incorporated into ASME Code, Section XI, IWB-2500, Item f in 2018.

Since many plants are operating beyond 40 years, and some plants intend to operate as long as 80 years, there is a need to extend the applicability for up to 80 years of operation. Furthermore, it is desirable to include feedwater nozzles in the technical basis. This paper provides the technical basis to update Code Case N-702 to be applicable for up to 80 years and includes feedwater nozzles. Other updates are also made to the evaluations to bring the analysis in-line with current industry standards.

A summary of the probabilistic fracture mechanics inputs and results are provided in this paper, which demonstrates the probability of failure is within NRC-approved acceptance criteria for each case analyzed. Several sensitivity studies were also performed in order to evaluate the impact of different inputs. Screening criteria is provided for each RPV nozzle including relevant operating parameters. This paper is intended to provide the technical basis for a revision to Code Case N-702-1.

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